1. Field of the Invention
This invention relates to a method for Hybrid Automatic Repeat Request reordering in Enhanced Uplink Dedicated Channel in WCDMA (Wideband Code Division Multiple Access) mobile communication system.
2. Description of the Related Art
Enhanced Up-link Dedicated Channel (simplified as EUDCH hereinafter) is a research project under standardization proposed by version 6 of 3rd Generation Partner Project (3GPP). The purpose of EUDCH is to improve the up-link capacity of the system through efficient management and planning for up-link transmission resources of the wireless network, and to make it applicable to the transmission of data service with high bursts. It improves the percentage of coverage and the throughput of the cell, improves uplink transmission rate as well as reduces uplink delay through improving the performance of uplink dedicated transfer channel. Main technologies adopted are as follows:                Adaptive modulation and coding scheme        Hybrid automatic repeat request protocol        Node B (Base Station) control and scheduling        Fast dedicated channel set-up        Short frame structure and improvement of the quality of service        Support of relevant physical layer and higher layer signaling        
Hybrid Automatic Repeat Request (HARQ) is one of the main technologies. This invention proposes the application method of the HARQ technology in EUDCH with emphasis on the operating method for reordering.
In the existing WCDMA mobile communication system, the standard about detailed operating method for HARQ in EUDCH doesn't exist yet. In principle, HARQ operation in EUDCH can be regarded as the inverse process of the HARQ operation in High Speed Data Packet Access (HSDPA). In the following, the relevant definition of the HARQ reordering in HSDPA will be explained.
FIG. 1 presents a structure of UE side MAC-hs (Medium Access Control—high speed) entity in HSDPA.
The MAC-hs handles the HSDPA specific functions. In the model below the MAC-hs comprises the following entities:
101 HARQ: The HARQ entity is responsible for handling the MAC functions relating to the HARQ protocol. The HARQ functional entity handles all the tasks that are required for hybrid ARQ. It is responsible for generating ACKs or NACKs. The detailed configuration of the hybrid ARQ protocol is provided by RRC over the MAC-Control SAP.
102 Reordering Queue distribution: The reordering queue distribution function routes the MAC-hs PDUs to the correct reordering buffer based on the Queue ID.
103 Reordering: The reordering entity reorders received MAC-hs PDUs according to the received TSN. MAC-hs PDUs with consecutive TSNs are delivered to the disassembly function upon reception. MAC-hs PDUs are not delivered to the disassembly function if MAC-hs PDUs with lower TSN are missing. There is one reordering entity for each Queue ID configured at the UE.
104 Disassembly: The disassembly entity is responsible for the disassembly of MAC-hs PDUs. When a MAC-hs PDU is disassembled the MAC-hs header is removed, the MAC-d PDUs are extracted and any present padding bits are removed. Then the MAC-d PDUs are delivered to higher layer.
The associated signalling shown in the figure illustrates the exchange of information between layer 1 and layer 2.
At the receiver, there are two buffers, i.e. a soft combining buffer at the physical layer and a re-ordering buffer at the MAC layer. The soft combining buffer is used to combine retransmissions and decode the data These two buffers are both located in the receiver, i.e. the UE (User Equipment).
If the existing HARQ reordering technology is applied to EUDCH, following two problems may be resulted in:
1) It is not preferable to dispose both soft combining buffer and reordering buffer at the Node B. Considering the case of soft handoff, each Node B in active set is receiving uplink data and the data correctly received by each Node B or not may be different. So it is unnecessary to set a reordering buffer at each Node B, which makes latency too long and results in delay in one aspect, and in another aspect may result in waste of the buffer space. Only if one Node B correctly receives the data, the data can be directly sent to the SRNC (Serving Radio Network Controller) and reordered uniformly at the SRNC, which can obtain the most effective diversity gain.2) In some cases, the reodering buffer can result in perpetual data loss and then result in the queue hole. In conclusion, following several situations may happen:                NACK is understood as ACK by mistake. In this case, the UE won't retransmit this packet but starts to transmit the new packets.        If the retransmission retry of the certain data is too large or the retransmission time reaches at the certain limitation, the UE will give up the retransmission and starts to send new data.        If the transmission of the certain data is preempted by other queue with higher priority, the UE will give up the retransmission and starts to send the new data.        
If preferable measure isn't adopted to deal with the above several cases, it will result in queue stop, thus correctly received data can't be sent upward and the buffer overflows.